In electroplating sometimes referred to as electrodeposition, a conductive item to be metal plated which forms a cathode, and an anode, are immersed in an electrolyte containing one or more dissolved metal salts, and a battery or rectifier supplies direct current. In one method the anode is of the plating metal and metal molecules of the anode are oxidised and dissolved into the electrolyte and at the cathode the dissolved metal ions are reduced and plated onto the cathode/item. In another method the anode is not consumable and ions of the plating metal are provided in the electrolyte and must be periodically replenished.
Electroless plating or deposition is a non-galvanic plating or coating method in which a reducing agent, typically sodium hypophosphite, in aqueous solution reduces metal ions of the plating metal in solution from the anode, which deposit onto the cathode/item. Electroless nickel plating may be used to deposit a coating of nickel Ni—P or Ni—B onto a substrate which may be a metal or plastic substrate.
Electroless plating may also be used to form a metal-ceramic composite coating on a substrate, such as an Ni—P—TiO2 coating for example. TiO2 nanoparticles are added to the electroless plating solution and co-deposit on the substrate with the Ni—P in an Ni—P—TiO2 matrix. The TiO2 particles can tend to agglomerate together in solution and thus distribute non-uniformly on the substrate thus giving uneven properties to the coating, and with the objective of reducing this the solution is continuously stirred and/or a surfactant is added to assure good dispersion of the TiO2 particles through the solution.
Ni—P—TiO2 coatings may also be formed on a substrate or item by first forming a coating of Ni—P on the item by electroplating and then dipping the item into a TiO2 sol to deposit TiO2 on/in the coating by the sol-gel process.
Plating or coating of an item or surface is typically carried out to provide a desired property to a surface that otherwise lacks that property or to improve a property to a desired extent, such as abrasion or wear resistance, corrosion resistance, or a particular appearance, for example.